Cobalt can catalyze the formation of acetaldehyde from methanol, carbon monoxide, and hydrogen, a reaction known as reductive carbonylation. For example, it was disclosed by Wender et al., Science, 113, (1951), 206-207, that a cobalt carbonyl catalyst system could be used. However, the product of the disclosed process was primarily ethanol, together with a small amount of acetaldehyde. It was later shown that the addition of iodide to a cobalt-containing catalyst system increased the amount of acetaldehyde produced. Iodide is typically added as a co-catalyst (also commonly referred to as a promoter) to the reaction in a form such as hydroiodic acid (a strong acid), methyl iodide, elemental iodine, or as an iodide salt such as lithium iodide or sodium iodide.
Homologation of methanol to ethanol can be achieved by addition of a hydrogenation catalyst, typically ruthenium based, to a reductive carbonylation system. For example, Mizoroki, et al., Bull. Chem. Soc. Japan, 52, (1979), 479-482, have described a catalyst system containing a cobalt compound, a ruthenium compound and methyl iodide to convert methanol to ethanol with 77% selectivity.
There is, however, a need to influence readily the relative amounts of aldehyde and/or alcohol produced in a reductive carbonylation reaction to maximize the desired product profile. In particular, methods of making aldehydes are desired. There is also a need for an inexpensive catalyst that can be used instead of the typical rhodium catalyst or iridium/ruthenium catalyst for the reductive carbonylation of alcohols.